The relation between bile acid metabolism and fat absorption in the perinatal period will be examined. For this purpose the state of preparedness of mechanisms of bile acid synthesis, excretion and intestinal absorption will be studied in near-term dogs and monkeys. This will be performed by: 1) measuring basal fetal bile acid excretion after drainage of the fetal bile acid pool; 2) by measuring the incorporation of labeled cholesterol into fetal bile acid; 3) by measuring placental transfer of bile acid from mother to fetus; 4) by in vitro and in vivo measurement of intestinal bile acid absorption. In addition, studies of bile acid metabolism and the relation between bile and fat absorption will performed in newborn infants. The pool size, and turnover and synthesis rates of bile acid will be determined by stable isotope technique. The absorption of lipid in the presence of micellizing bile acid will be measured.